Curriculum

17 Sections
1548 Lessons
100 Days

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U01.01 Biochemistry
This biochemistry review for USMLE Step 1 covers essential topics including metabolism, enzymology, and molecular biology.
126
U01.02 Immunology
Prepare for USMLE Step 1 Immunology with a comprehensive review covering foundational concepts, immune system mechanisms, and key disorders to solidify your understanding and boost exam readiness.
42
U01.03 Microbiology
Review essential microbiology topics for the USMLE Step 1, covering key pathogens, mechanisms of disease, and antimicrobial principles critical for mastering infectious disease concepts.
172
U01.04 General Pathology
Explore key concepts in general pathology essential for the USMLE Step 1. This review covers fundamental principles, disease mechanisms, and clinical correlations to help you excel in your medical exam.
35
U01.05 Pharmacology
Master key pharmacology concepts for the USMLE Step 1 with a focus on drug mechanisms, therapeutic uses, adverse effects, and interactions essential for high-yield exam performance.
43
U01.06 Public Health Sciences
Review essential Public Health Sciences topics for the USMLE Step 1, covering epidemiology, biostatistics, health policy, and ethics to strengthen your understanding of foundational public health principles.
53
U01.07 Cardiovascular system
Comprehensive review of essential cardiovascular system topics to help you excel in the USMLE Step 1 exam, covering key concepts from anatomy to pathology.
73
U01.08 Endocrine system
Master essential concepts of the endocrine system for USMLE Step 1, covering hormone regulation, feedback mechanisms, and key disorders to boost your exam readiness.
51
U01.09 Gastrointestinal system
Review key topics in the gastrointestinal system for the USMLE Step 1, covering essential concepts in anatomy, physiology, pathology, and pharmacology to reinforce your understanding and test readiness.
131
U01.10 Hematology and Oncology
This review covers essential Hematology and Oncology topics for the USMLE Step 1, including hematopoiesis, coagulation, anemias, leukemias, lymphomas, and neoplastic syndromes.
148
U01.11 Musculoskeletal, Skin, and Connective Tissue
Review essential topics for the USMLE Step 1 Musculoskeletal, Skin, and Connective Tissue systems, covering anatomy, physiology, pathology, and pharmacology fundamentals critical for exam success.
178
U01.12 Neurology and Special Senses
Master the foundational concepts of Neurology and Special Senses with our USMLE Step 1 review, covering essential topics like neuroanatomy, neurophysiology, and sensory pathways.
143
U01.13 Psychiatry
Psychiatry for the USMLE Step 1 focuses on understanding the pathophysiology, diagnosis, and treatment of psychiatric disorders, with an emphasis on key concepts like neurotransmitter imbalances, mental health disorders, and pharmacology.
83
U01.14 Renal System
The Renal System review for USMLE Step 1 covers key concepts including renal physiology, nephron function, acid-base balance, electrolyte regulation, and renal pathology, crucial for understanding both normal and abnormal kidney functions.
81
U01.15 Reproductive System
The USMLE Step 1 Reproductive System review covers key concepts in human reproduction, including anatomy, physiology, endocrinology, and common pathologies affecting both male and female reproductive health.
124
U01.16 Respiratory System
The Respiratory System review for the USMLE Step 1 covers key concepts in anatomy, physiology, pathophysiology, and pharmacology essential for understanding respiratory diseases and treatments.
61
U01.17 Rapid Review
he USMLE Step 1 Rapid Review covers essential topics across multiple disciplines, providing a concise, high-yield overview to reinforce key concepts and optimize your exam preparation.
5

Stains

Staining techniques are essential tools for identifying and differentiating microorganisms. This guide provides an overview of various stains used in bacterial identification, along with their applications.

1. Gram Stain

Purpose

Gram staining is the first-line laboratory test used for bacterial identification. It distinguishes bacteria based on the structural differences in their cell walls.

Principle

Gram-positive bacteria (Gram ⊕): Have a thick peptidoglycan layer that retains the crystal violet dye, appearing purple.
Gram-negative bacteria (Gram ⊝): Have a thin peptidoglycan layer and do not retain the crystal violet dye. They take up the counterstain (safranin) and appear red or pink.

Bacteria That Do Not Stain Well

Certain bacteria do not gram stain effectively due to unique characteristics. These include:

Bacteria	Reason for Poor Gram Staining
Treponema, Leptospira	Too thin to be visualized under a microscope
Mycobacteria	High lipid content in the cell wall
Mycoplasma, Ureaplasma	Lack of a cell wall
Legionella, Rickettsia, Chlamydia, Bartonella, Anaplasma, Ehrlichia	Primarily intracellular; Chlamydia lacks muramic acid, affecting the peptidoglycan layer

Bacteria That Do Not Stain Well

Mnemonic to Remember

“These Little Microbes May Unfortunately Lack Real Color But Are Everywhere”:

Treponema
Leptospira
Mycobacteria
Mycoplasma
Ureaplasma
Legionella
Rickettsia
Chlamydia
Bartonella
Anaplasma
Ehrlichia

2. Giemsa Stain

Purpose

The Giemsa stain is used to detect intracellular pathogens, including certain bacteria and protozoa.

Organisms Stained

Rickettsia
Chlamydia
Trypanosomes
Plasmodium
Borrelia
Helicobacter pylori

Mnemonic to Remember

“Ricky got Chlamydia as he Tried to Please the Bored Hot Geisha.”

Rickettsia
Chlamydia
Trypanosomes
Plasmodium
Borrelia
Helicobacter pylori

3. Periodic Acid–Schiff (PAS) Stain

Purpose

The PAS stain is used to identify glycogen and mucopolysaccharides, making it useful in diagnosing conditions like Whipple disease.

Organisms Stained

Tropheryma whipplei (Whipple disease)

Mnemonic to Remember

“PaSs the sugar” – indicating its use in staining glycogen-rich structures.

4. Ziehl-Neelsen Stain (Carbol Fuchsin)

Purpose

Used to detect acid-fast bacteria, which retain the stain due to the high lipid content of their cell walls. It’s also useful for identifying certain protozoa.

Organisms Stained

Mycobacteria
Nocardia
Cryptosporidium (protozoa)

Alternative Stain

Auramine-rhodamine stain is more sensitive and cost-effective for screening.

5. India Ink Stain

Purpose

The India ink stain is primarily used to visualize the thick polysaccharide capsule of Cryptococcus neoformans. Mucicarmine stain can also be used to stain the capsule red.

Organism Stained

Cryptococcus neoformans

6. Silver Stain

Purpose

Silver stains are used to detect a variety of organisms, especially fungi and certain bacteria.

Organisms Stained

Fungi (e.g., Coccidioides, Pneumocystis jirovecii)
Legionella
Helicobacter pylori

7. Fluorescent Antibody Stain

Purpose

This stain is used to identify a wide range of microorganisms, including bacteria, viruses, protozoa, and fungi. The fluorescent tag helps in visualization.

Example

FTA-ABS: A specific test used to diagnose syphilis by detecting Treponema pallidum.

Points to Remember

Gram staining is a key initial test in identifying bacterial species based on cell wall structure.
Some bacteria, like Mycobacteria and Treponema, require special stains due to unique cell characteristics.
Mnemonics can help in recalling organisms that are difficult to stain using standard methods.

Bibliography

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USMLE Step 1 Review Series

Curriculum

Stains

1. Gram Stain

Purpose

Principle

Bacteria That Do Not Stain Well

Mnemonic to Remember

2. Giemsa Stain

Purpose

Organisms Stained

Mnemonic to Remember

3. Periodic Acid–Schiff (PAS) Stain

Purpose

Organisms Stained

Mnemonic to Remember

4. Ziehl-Neelsen Stain (Carbol Fuchsin)

Purpose

Organisms Stained

Alternative Stain

5. India Ink Stain

Purpose

Organism Stained

6. Silver Stain

Purpose

Organisms Stained

7. Fluorescent Antibody Stain

Purpose

Example

Points to Remember

Bibliography

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